The Taliban are planning a major winter offensive combining their diverse factions in a push on the Afghan capital, Kabul, intelligence analysts and sources among the militia have revealed.

The thrust will involve a concerted attempt to take control of surrounding provinces, a bid to cut the key commercial highway linking the capital with the eastern city of Jalalabad, and operations designed to tie down British and other Nato troops in the south.

Last week Nato, with a force of 40,000 in the country including around 5,000 from Britain, said it had killed 48 more Taliban in areas thought to have been 'cleared'. 'They have major attacks planned all the way through to the spring and are quite happy for their enemy to know it,' a Pakistan-based source close to the militia told The Observer. 'There will be no winter pause.' The Taliban's fugitive leader, Mullah Omar, yesterday rejected overtures for peace talks from President Hamid Karzai and said it intended to try him in an Islamic court for the 'massacre' of Afghan civilians.

Since their resurgence earlier this year the Taliban have made steady progress towards Kabul from their heartland in the south-east around Kandahar, establishing a presence in Ghazni province an hour's drive from the suburbs. They do not expect to capture the capital but aim to continue destabilising the increasingly fragile Karzai government and influence Western public opinion to force a withdrawal of troops. 'The aim is clear,' said the source. 'Force the international representatives of the crusader Zionist alliance out, and finish with their puppet government.'

A winter offensive breaks with tradition. 'Usually all Afghans do in the winter is try and stay warm,' said a Western military intelligence specialist in Kabul. 'The coming months are likely to see intense fighting, suicide bombings and unmanned roadside bombs. That is a measure of how much the Taliban have changed.'

The new Taliban, a rough alliance of Islamist zealots, teenagers seeking adventure, disgruntled villagers led by tribal elders alienated from the government, drug dealers and smugglers - is no longer the parochial, traditional militia that seized Kabul almost exactly 10 years ago and was ousted by the American-led coalition in 2001. Tactics, ideology, equipment and organisation have all moved on. The use of suicide bombings, roadside bombs and targeted assassinations of those cooperating with Western forces are methods copied from Iraqi insurgents.

'They can't engage in big groups so... they've moved on to these targeted assassinations,' said Naimatullah Khan, deputy chief of the local council in southern Kandahar province, who has seen several colleagues killed. More than 70 suicide bombings, four times as many as last year, have together killed scores of civilians. In 2001 the tactic was almost unknown among Afghans. French intelligence sources say militants are heading to Afghanistan rather than Iraq.

The Taliban are now exploiting modern propaganda such as recruitment videos and mass-produced DVDs and CDs. This has been copied from international terrorist operators such as Osama bin Laden, thought to be hiding either in the eastern zones along the Afghan border with Pakistan or in the heavily wooded northern province of Kunar where there is continued skirmishing between US troops and militants. Civilian deaths - such as the 50 reported during Nato operations last week near Kandahar - are eagerly exploited for propaganda.

The Taliban remain a local phenomenon and are not believed to be in close liaison with the Saudi-born bin Laden or his Egyptian-born associate Ayman al-Zawahiri. 'It is more an ad hoc co-operation between the Arabs and some of the major figures in the broad Taliban movement, especially in the east,' said a French intelligence source. Those fighting British troops in Helmand province are thought to be linked to major clerics and traffickers in Pakistan.

In the south, the Taliban's strategy has been influenced by the doctrine of Pakistani spymasters who ran the insurgent war against the Russians in the 1980s. 'The idea then was to keep Afghanistan just below boiling point,' said one Pakistan-based veteran of the 'jihad' against Moscow's troops. 'The Taliban don't want an apocalyptic explosion of violence. They want a steady draining of the West's resources, will and patience.'

The Pakistani influence on the Taliban strategy does not surprise many observers. Senior Nato officials speak privately about 'major Taliban infrastructure' in the neighbouring country but Western military intelligence analysis has consistently underestimated the group's depth and breadth - it can almost be considered the army of an unofficial state lying across the Afghan-Pakistani frontier that has no formal borders but is bound together by ethnic, linguistic, ideological and political ties.

Centred on areas dominated by Pashtun tribes, 'Talibanistan' stretches from the Indus river to the mountainous core of Afghanistan and comprises tens of millions of people who, as well as language and traditions, increasingly share an ultra-conservative form of Islam.

A political party linked to the Taliban is in power in the two most western provinces of Pakistan. There are powerful commercial lobbies tied to smuggling of drugs and other commodities, while mainstream businesses such as timber and textiles provide vast amounts of cash which can be funnelled into military operations. 'The problem for the Nato planners is that the Taliban have a safe rear area, cash, arms supplies and the support of much of the population,' said a Western diplomat in Islamabad. 'That's all a successful guerrilla army needs.'

Western soldiers and political leaders insist on the need to win over hearts and minds, but many local observers believe that, at least in the south of Afghanistan, the opportunity offered by the defeat of the Taliban in 2002 to bring security and development to this strategically critical and opium-rich area has been missed.